1. Field of the Invention
This invention pertains to cigarette manufacture and, in particular, to a method and apparatus for controlling cigarette firmness during such manufacture.
2. Description of the Prior Art
In the manufacture of cigarettes, various practices have been employed at the cigarette maker to provide continuous control over cigarette rod parameters. Thus, for example, systems have been proposed for monitoring rod tobacco density and using monitored density to control cigarette rod tobacco content. British Specification No. 1,376,747 discloses one such system in which microwave energy is utilized to detect rod tobacco density. In this system, since the microwave energy employed is affected by moisture as well as tobacco, two separate signals are generated, each signal being dependent upon the tobacco mass and the water mass in the cigarette rod. These signals are used to derive the individual tobacco and water mass values.
Another type of practice at the cigarette maker involves control of the maker to provide a preselected or target firmness for the issuing cigarette rod. In this practice, rod firmness is detected by a suitable firmness sensor which might comprise a plurality of mechanical contiguous feelers, or non-contiguous pneumatic or electrical devices. Such practice further contemplates comparing the detected firmness with the target firmness to develop an error signal for controlling the tobacco content provided by the maker to the rod. Thereby, rod firmness is made to approach target firmness in typical control system fashion. Systems of this general type are disclosed, for example, in U.S. Pat. Nos. 3,411,513; 3,595,067 and 3,850,029.
Attendant on the latter practice is variation of tobacco content for cigarette rod firmness variations due not only to tobacco character changes but also to moisture content changes. Effecting control in this manner is wasteful of tobacco and prohibits cigarette maker operation at maximum efficiency.
It is therefore a primary object of the present invention to provide a method and apparatus for controlling cigarette firmness in a manner which promotes cigarette maker efficiency.
It is a further object of the present invention to provide a method and apparatus which avoids excessive addition and/or subtractions of tobacco during cigarette maker operation.